1. Field of the Invention
The present invention relates to a driving technique of a transport roller in an ADU in which after one-sided recording is continuously made on plural sheets, the sheets are not stacked but are reversed in the middle of transport, and then, the sheets are again transported to an image forming unit, and recording is made on the second side.
2. Description of the Related Art
Hitherto, as an automatic duplexing unit (hereinafter ADU) transport roller driving device, there is an example (JP-A-2005-89073) in which a first, a second and a third transport rollers are disposed in a re-paper feed transport path, part of the first and the second transport rollers are drive-coupled through one-way clutches to one motor capable of forwardly and reversely rotating, the other end of the first transport roller is drive-coupled to the other ends of the second and the third transport rollers through one-way clutches so that they are mutually rotated in the same direction, and when the motor is forwardly rotated, all the transport rollers are rotation-driven in a sheet transport direction, and when the motor is reversely rotated, only the first transport roller is rotation-driven in the sheet transport direction, and the second and the third transport rollers are stopped.
In the case of the structure as stated above, for example, in the case where the waiting time of a sheet at a registration roller becomes longer than usual because the amount of writing of images on a photoconductive drum is larger than usual, the second and the third transport rollers are stopped, and only the first transport roller is rotation-driven, so that only a succeeding sheet can be transported. However, even if a warp occurs on the succeeding sheet between the first and the second transport rollers during this operation, since switching is performed only between two patterns, that is, all the transport rollers are rotation-driven or only the first transport roller is rotation-driven, and the warp on the succeeding sheet can not be removed.